57 2 
SEMI VER TERRA TES. 
Tailed Ascidians. 
ment. Usually, the family is divided into the two genera Salpa and Cyclosalpa, the 
latter being distinguished by having the digestive tract coiled up; but some writers 
have divided the first of these two into several subgeneric groups. A second family 
is represented by the very imperfectly known genus Octacnemus, dredged at depths 
of between one and two thousand fathoms in the South Pacific; the body being 
much flattened, and probably attached by one extremity. Nothing is known as 
to the life-history of this singular form. 
The second suborder—Cyclomyaria—of the free-swimming non-luminous as¬ 
cidians takes its name from the muscular bands of the inner tunic forming perfect 
rings, and is typically represented by the genus Doliolum. The life-history is 
complicated by polymorphism; the tailed larva developing into a sexless form, 
the buds from which give rise to nutritive units, fostering units, and reproductive 
units. In the typical genus all the muscles form encircling hoops, and the three 
forms of the sexual generation occur together on one stolon, or outgrowth; but in 
Anchinia there are only two complete muscular rings, and the three forms of the 
sexual generation are produced successively. 
The free-swimming form known as Appendicularia is the type 
of the third and last order—Larvacea—of the class, all the members 
of which are characterised by the possession in the adult state of large tail-like 
appendages, furnished with a skeletal axis. These creatures, which are of minute 
size, have not undergone the degeneration so noticeable in the adult of the other 
tunicates, and thus correspond much more closely to the larval stage of the latter. 
A curious feature is the rapid production of a temporary outer tunic, which may 
be shed at any time, and replaced by a second one. There is no separate atrial 
cavity; and the branchial chamber is simply an elongated pharynx, with two 
openings on the lower surface, which correspond to the gill-slits, and are well 
furnished with cilia. The nervous system consists of a large ganglion placed in 
the anterior part of the dorsal surface, followed by a long chord, provided 
with smaller ganglia, and extending backwards over the intestine to reach the 
tail, where it runs along the left side of the skeletal axis. The intestine itself is 
situated behind the branchial chamber, and the vent opens on the inferior or 
ventral aspect of the body in advance of the gill-slits. Neither budding, meta¬ 
morphosis, nor alternation of generations takes place; and the reproductive organs 
are situated at the hinder end of the body. The group comprises only the single 
family Appendiculariidce, which contains five genera, the names and characters 
of which it will be unnecessary to mention. 
Botryllus (nat. size and enlarged). 
